Microsoft’s Windows Phone 8 platform has slowly increased its market share since being released last October. The latest numbers from Kantar Worldpanel found that the operating system accounted for 5.6% of sales in the United States in the first quarter of 2013, up 1.9 percentage points from the same period in 2012. Android smartphones continue to dominate the market, increasing 1.4 percentage points and accounting for 49.3% of all smartphone sales, compared to the iPhone’s market share, which fell from 44.6% in Q1 2012 to 43.7% last quarter.

“As iOS and Android continue to battle it out for top-selling smartphone OS, we have seen Windows steadily grow over the past year and is now at its highest sales share figure so far,” Kantar Worldpanel ComTech analyst Mary-Ann Parlato said. “Windows strength appears to be the ability to attract first time smartphone buyers, upgrading from a feature phone.”

First time smartphone buyers accounted for 52% of Windows Phone customers, while 55% of iPhone users and 51% of Android buyers upgraded from another smartphone.

“While the differences between these figures are small, with over half of the US market still owning a feature phone, it’s likely that many will upgrade over the coming year, which will ultimately contribute to more growth for the Windows brand.” Parlato added.

Nokia has benefited greatly from increased Windows Phone sales, accounting for 4% of smartphones sold in the first quarter, up from just 1% in 2012. The firm notes, however, that Android smartphone sales are expected to spike in the second quarter with the release of devices like the Galaxy S4 and HTC One.